On 1/23/23 09:30, David Howells wrote:
Provide a helper in the get_user_pages code to drop a pin or a ref on a
page based on being given FOLL_GET or FOLL_PIN in its flags argument or do
nothing if neither is set.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
cc: Christoph Hellwig <hch@xxxxxx>
cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
cc: linux-fsdevel@xxxxxxxxxxxxxxx
cc: linux-block@xxxxxxxxxxxxxxx
cc: linux-mm@xxxxxxxxx
---
include/linux/mm.h | 3 +++
mm/gup.c | 22 ++++++++++++++++++++++
2 files changed, 25 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8f857163ac89..3de9d88f8524 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1367,6 +1367,9 @@ static inline bool is_cow_mapping(vm_flags_t flags)
#define SECTION_IN_PAGE_FLAGS
#endif
+void folio_put_unpin(struct folio *folio, unsigned int flags);
+void page_put_unpin(struct page *page, unsigned int flags);
How about these names instead:
folio_put_or_unpin()
page_put_or_unpin()
?
Also, could we please change the name of the flags argument, to
gup_flags?
+
/*
* The identification function is mainly used by the buddy allocator for
* determining if two pages could be buddies. We are not really identifying
diff --git a/mm/gup.c b/mm/gup.c
index f45a3a5be53a..3ee4b4c7e0cb 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -191,6 +191,28 @@ static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
folio_put_refs(folio, refs);
}
+/**
+ * folio_put_unpin - Unpin/put a folio as appropriate
+ * @folio: The folio to release
+ * @flags: gup flags indicating the mode of release (FOLL_*)
+ *
+ * Release a folio according to the flags. If FOLL_GET is set, the folio has a
+ * ref dropped; if FOLL_PIN is set, it is unpinned; otherwise it is left
+ * unaltered.
+ */
+void folio_put_unpin(struct folio *folio, unsigned int flags)
+{
+ if (flags & (FOLL_GET | FOLL_PIN))
Another minor complication is that FOLL_PIN is supposed to be an
internal-to-mm flag. But here (and in another part of the series), it
has leaked into the public API. One approach would be to give up and
just admit that, like FOLL_GET, FOLL_PIN has escaped into the wild.
Another approach would be to use a new set of flags, such as
USE_FOLL_GET and USE_FOLL_PIN.
But I'm starting to lean toward the first approach: just let FOLL_PIN be
used in this way, treat it as part of the external API at least for this
area (not for gup/pup calls, though).
So after all that thinking out loud, I think this is OK to use FOLL_PIN.
+Cc Jason Gunthorpe, because he is about to split up FOLL_* into public
and internal sets.
thanks,
--
John Hubbard
NVIDIA
